The present invention relates generally to transfer cases for use in four-wheel drive vehicles and, more particularly, to a variable ratio torque transfer coupling for transfer cases.
In general, power transfer mechanisms, such as transfer cases, are operatively associated with both manual and automatic transmissions for directing power to the non-driven wheels of a motor vehicle for establishing a four-wheel drive mode. Many automotive transfer cases are now equipped with a torque transfer assembly that is capable of automatically shifting (xe2x80x9con-demandxe2x80x9d) between the two-wheel drive mode and the four-wheel drive mode. Examples of on-demand transfer cases incorporating torque transfer coupling are shown in U.S. Pat. Nos. 5,215,160; 5,443,426; 5,400,866; 5,597,369; 6,041,903; and 6,112,874. While such on-demand transfer cases have proven to provide enhanced traction control compared to traditional part-time transfer cases, the need exists for continued development of improved torque transfer systems.
In view of the foregoing, it is an object of the present invention to provide a unique torque transfer system for use in vehicular power transfer assemblies which can continuously vary the torque transferred from an input member to an output member;
It is another object of the present invention to incorporate the variable torque transfer system into on-demand transfer cases for use in four-wheel drive vehicles.
As a related object, the variable torque transfer system can be arranged to permit the vehicle operator to select between distinct two-wheel and four-wheel drive modes or operate in an adaptive mode where the torque transfer is automatically varied in response to vehicular operating and/or road conditions to improve the vehicle""s tractive performance.
Accordingly, the torque transfer system of the present invention includes a variable drive mechanism for selectively rotating a component of a geared differential unit to vary the torque transferred from the input member to the output member. More particularly, drive mechanism includes a unique worm/worm gear transmission which is operatively coupled to a carrier member of the differential unit. When the drive mechanism is held fixed, the carrier does not rotate and there is no reduction between the input and output members. However, rotation of the drive mechanism causes the carrier to rotate relative to the input member which functions to change the percentage of the total torque transferred to the output member. By varying the relative rotational velocity of the carrier member it is possible to vary the torque transfer ratio of the transfer case and provide a variable on-demand system. Preferably, the drive mechanism includes a variable speed motor having an output arranged to drive the worm/worm gear transmission so as to control rotation of the carrier associated with the differential unit. An electronic control system is provided to control actuation of the motor in response to certain operating characteristics of the vehicle.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.